The present invention relates to new derivatives of hyaluronic acid, a process for their preparation and the cosmetic or pharmaceutical compositions containing such products.
Hyaluronic acid is a mucopolysaccharide that is present almost in each part of a living organism and in particular in the skin. Chemically, hyaluronic acid is formed by straight polymer chains having a molecular weight ranging from hundreds thousand to millions dalton, including repeated disaccharid units constituted by N-acetyl glucosamine and glucoronic acid bound to each other by glucosidic bonds. Hyaluronic acid has the capacity of binding high amounts of water coming from the capillary network, necessary to keep in a solution form the catabolites, electrolytes and gases that spread from the capillaries to the cells and vice-versa, through the interstitial fluid. This phenomenon is of the essential to maintain the skin elastic and in a gelatinous physical condition. Hence, hyaluronic acid has a basic role in the control of the diffusion of nutrients, hormones, vitamins and inorganic salts of the connective tissue and in the removal of metabolism wastes which may give rise to reactions of an inflammatory type. As age increases, the amount of hyaluronic acid present in the organism decreases as well as its polymerization level, which results in a reduction in retained water, the skin shows alterations of its physical condition and undergoes an aging process that causes an increase in the fibrous part with respect to the elastic one.
There are at present known cosmetic preparations that are mainly used as moisturizers or age retarding preparations, based on low molecular weight hyaluronic inorganic salts. Such preparations have the drawback of utilizing low molecular weight hyaluronic acid, which is much less effective compared to high molecular weight hyaluronic acid. On the other hand, high molecular weight hyaluronic acid is scarcely soluble, which creates severe technical problems in the preparation of cosmetic and pharmaceutical formulations. As a consequence, the need is still felt of providing derivatives of hyaluronic acid having a high effectiveness in the cosmetic and pharmaceutical field, and having also chemical-physical characteristics such as to allow their use in different types of formulations. The present invention relating to high molecular weight new derivatives of hyaluronic acid solves these problems.
From one of these aspects, the present invention relates to new salts between high molecular weight hyaluronic acid and at least one natural amino acid. Preferred salts are those wherein the amino acid is selected from among lysine, arginine, methionine or aspartic acid. Particularly advantageous is lysine yaluronate which we gave the invention name Yalyse and which will be indicated in the future by the mark xe2x80x9cYALYSExe2x80x9d.
By the expression xe2x80x9chigh molecular weight hyaluronic acidxe2x80x9d, there is intended to indicate a hyaluronic acid having a molecular weight comprised between 1.5 and 3 million dalton.
The use of these new derivatives of hyaluronic acid in the cosmetic and pharmaceutical field provides remarkable advantages with respect to the known art. First of all, high molecular weight hyaluronic acid has the capacity of binding water amounts much higher than low molecular weight hyaluronic acid, promoting thereby a better diffusion of the dissolved substances and a greater elasticity of the skin. Besides this, the compounds of the present invention are constituted by hyaluronic acid salts with a counterion that can exercise a synergetic action with the yaluronate. In fact, as is known, amino acids carry out an essential role in the formation of special substances of skin physiology, such as melanin and keratin.
Of particular importance is lysine, which is basic in the biosynthesis of melanin, as well as the collagen of elastin and reticulin which are the main proteic skin components. The derivatives of the present invention are therefore capable of markedly reducing skin aging through an increase moisturizing of the dermis, a promoted cellular recycling and a stimulation of the synthesis of elastin as well as of free radicals.
From another of its aspects, the present invention relates to a process for the preparation of salts selected from among hyaluronic acid and at least a natural amino acid, characterized in that hyaluronic acid or a salt thereof is caused to react with at least a natural amino acid, in the form of a free base or in a salified form, respectively.
According to an advantageous aspect, the present invention relates to a process for the preparation of lysine hyaluronate, characterized in that sodium hyaluronate is reacted with lysine hydrochloride. Preferably, such reaction is carried out by suspending sodium hyaluronate in water and stirring until it gels before adding lysine hydrochloride.
The preparation reactions of the salts subject matter of the present patent application may be carried out using a stochiometric amount of the reagents or an excess of either component, in which latter case one obtains the salt and an excess reagent co-ordination through hydrogen bonds. By the expression xe2x80x9cstochiometric amounts of the reagentsxe2x80x9d there is intended to indicate that the number of amino acid moles used is equal to the number of the carboxy functions that are present in hyaluronic acid.
The possibility of varying the ratio of acid moles to amino acid moles allows to modulate the characteristics of the products obtainable as a function of the desired properties.
Organic molecules of various type may be coordinated to the products obtained according to the aforesaid processes by means of hydrogen bonds.
This allows to obtain end products having variable chemical-physical and pharmacological properties.
From another of its aspects, the present invention relates to the use of new high molecular weight hyaluronic acid salts in the cosmetic field.
From a further aspects the present invention relates to the use of the new high molecular weight hyaluronic acid salts as medicaments.
The active principles of the present invention are adapt to be formulated with suitable excipients, for instance those usually utilized is the cosmetic field, such as bee-wax, jujube oil, isostearyl isostearate, fatty acid, triglycerides, propylen glycol, lauryl alcohol, and hydroxypropylmethyl cellulose. Stabilizers, antioxidants, and preservatives, either individually or combined with each other, may be added to these active principles. Suitable stabilizers include Acepur K, Abiol, Prevan, Fondix G, BHA, BHT. Suitable antioxidants include butylhydroxyanisole, citric acid, tocopherol, sodium thiophosphate. Suitable preservatives include p-hydroxybenzoic acid esters or imidazolidinyl urea.
A preferred composition of the invention is in the one that comes in the form of an emulsion. Emulsions containing 1% to 5% lysine hyaluronate (Yalyse) are particularly preferred. Such compositions, either in the pure form or in the form of lyophilized sheets, are used in the treatment of burn wounds, decubitus ulcers, venous ulcers, and in all cicatrization processes. They may be also advantageously used in aesthetic surgery, especially following epidermis abrasion laser therapy interventions, in order to achieve a quicker and optimum re-epithelization.
Another preferred composition of the present invention in the one that comes in the form of a lotion. Particularly advantageous are the lotions comprising 1 % to 7% arginine hyaluronate, possibly mixed with glycolic acid and carrier substances and suitable excipients compatible with the type of utilization desired. Such lotions may be employed in alopecia cases due to excess sebum production, in allergy-based scalp hyperkeratoses, and in dandruff persistent cases.
A further type of preferred composition of the present invention is the one that comes in the form of a cream. Particularly advantageous are creams based on 1% to 7% lysine hyaluronate (Yalyse), possibly mixed with one or more substances selected from among vitamin A, vitamin E, ascorbic acid, cogic acid, allantoin, echinaceous calendula, xe2x80x9ccentellaxe2x80x9d, horsetail, persea, propolis, aloe, cera alba, arachis, zea mays, horse chestnut, ginko biloba, jujube, shea butter, bee-wax, hazelnut, sunflower, and with excipients compatible with its specific utilization. Thanks to their moisturizing action, such creams are particularly useful in reducing the process of skin-aging, in the treatment of wrinkles, dryness, opacity, and in promoting skin elasticity and luminosity. These creams may also be used as protectors in photodermatosis, as anti-erythema and, together with cogic acid or hydroquinone, in the treatment of senile spots.
From a last aspect, the invention relates to the use of new high molecular weight hyaluronic acid salts for the preparation of medicaments suitable for the treatment or prevention of a pathologic condition selected from among psoriasis, eczema, ichthyiosis, postactinic radiodermatosis, hemorrhoids, proctitis, hemorrhagic proctitis, atopic dermatitis, trophic ulcers and decubitus ulcers, sudamina, epidermophytosis or, generally, in the cases of prurigo. In these cases, the pharmaceutical compositions may possibly also include one or more substances selected from among salicylic acid, ascorbic acid or retynyl palmitate.